Cardiopulmonary bypass and heart transplant are two important surgical procedures used by cardiac surgeons. While they both are designed to improve cardiac functional status, the techniques could be greatly improved. In both cases, the procedures require that the hearts be removed from the normal circulation of the body and thus by definition, some degree of damage may be observed. In bypass and transplant, cardioplegic solution, rather than blood, are employed to perfuse the coronary arteries. Accordingly, the conditions and attendant risks/damage resulting from these procedures may differ from coronary stenosis induced damage. To reduce the degree of surgical damage, the hearts are perfused in a retrograde fashion with a cardioplegic solution designed to reduce energy needs of the tissue by arresting the hearts, making them hypothermic (reduce energy demands) and also supplying them with essential substrates. While such solutions are helpful, further improvements in the ability of these hearts to compensate for the surgical damage would be useful. Cardiopulmonary bypass involves aortic cross-clamping and retrograde infusion of cardioplegic solution while heart transplant involves removal of the heart from a donor and the heart is stored in cardioplegic solution or is retrogradely perfused using a Langendorff type system until transplant can be affected.
It has long been known that potassium leaks out of myocardial cells during ischemia and the amount of potassium which leaks out seems to be correlated with the degree of ischemic damage. Indeed, potassium leaks out of hearts subjected to the type of global ischemia which would be seen during cardiopulmonary bypass and heart transplant. Current thinking indicates that compounds which could block the outward flux of potassium, i.e., potassium channel blockers, could protect the ischemic tissue.